Parsec is game-streaming software that allows you to play local-multiplayer games online, and it works amazingly well! Here's some info on how to get started: https://youtu.be/6VBJf0C_JjE?t=54s

I've been running game nights every weekend for my own similar fan-game, here's some basically lag-free online gameplay: https://youtu.be/E6YYLSxbGyI (the host has no lag, joining players may have lag depending on their download speed and distance from the host...you'll want at least 10 download speed probably)

If you want to play Super Mario War or Super Clash Bros or any other local multiplayer games online, you can join the Super Clash Bros Discord server or the Parsec Discord server to find players. Soon though Parsec will release their new Party Finder feature out of beta, which lets you host parties for others to find right inside Parsec, that way you don't have to arrange matches on Discord.